The proteoglycan 4 (prg4) gene codes for highly glycosylated proteins termed megakaryocyte stimulating factor (MSF), lubricin, and superficial zone protein (SZP). Lubricin was first isolated from synovial fluid and demonstrated lubricating ability in vitro similar to synovial fluid at a cartilage-glass interface. Lubricin was later identified as a product of synovial fibroblasts. O-linked β(1-3)Gal-GalNAc oligosaccharides within a large mucin like domain of 940 amino acids, encoded for by exon 6, have also been described. SZP was first localized at the surface of explant cartilage from the superficial zone and isolated from conditioned medium. These molecules (as well as O-linked proteoglycans thereof) are collectively referred to herein as PRG4. PRG4 has been shown to be present inside the body at the surface of synovium, tendon, and meniscus, but there has been no description of using PRG4 as a lubricant for the purposes described herein.